In industry, silica gel is traditionally used as adsorbent. It is used to adsorb vapors, e.g., from petrol, benzene, ether, alcohol, from air, e.g., in the celluloid-, silk-, lacquer- and explosives-factories. Silica gel is a good desiccant; it can be used for gases, liquids and even solids can be dried (e.g. in a desiccator), liquids and lipids can be purified and decolorized. Silica gel can be used as a support medium for catalysts, as deodorant, and as drying material, as well as an active ingredient in filtertips for cigarettes. It is also used to coat electrodes in electrochemical cells or accumulators. Other fields of application comprise lacquer, synthetic materials, adhesives, toothpaste, etc.
In chemistry, silica gel is used, e.g., in chromatography as a stationary phase. In column chromatography the stationary phase is most often composed of silica gel particles of 1.5-60 μm. In this application, due to silica gel's polarity, non-polar components tend to elute before more polar ones. Lipophilic groups may be attached to the silica gel surface to produce a reverse phase silica gel which elutes polar components first. Silica gel is also applied to aluminum or plastic sheets for thin layer chromatography. For high-performance liquid chromatography (HPLC) in the fields of proteomics, metabolomics and phytomics silicate materials are also frequently used. In order to achieve the highest separation efficiencies, the physical properties of silica particles such as particle size, pore volume and surface area play an essential role.
The size of the particles is usually determined by electron microscopy, light scattering or the Coulter-Counter method, the surface area is measured by nitrogen adsorption experiments according to the Brunnauer Emmet Teller (BET) theory, pore sizes and volumes are usually assessed by size exclusion chromatography (SEC).
Nanotechnology is a field of applied science focused on the design, synthesis, characterization and application of materials on the nanoscale, so called nanomaterials. Nowadays nanomaterials play important roles in colloidal science, biology, physics, chemistry and other scientific fields that involve the study of phenomena and manipulation of material at the nanoscale and serve essentially to extend existing sciences into the nanoscale.
Two main approaches exist to produce nanomaterials: one is a “bottom-up” approach where materials are built up atom by atom, the other a “top-down” approach where they are synthesized or constructed by removing existing material from larger entities.
A unique aspect of nanomaterials is the vastly increased ratio of surface area to volume, which opens new possibilities in surface-based science, such as catalysis. This catalytic activity also opens potential risks in their interaction with biomaterials.
The impetus for nanotechnology has stemmed from a renewed interest in colloidal science, coupled with a new generation of analytical tools such as the atomic force microscope (AFM) and the scanning tunneling microscope (STM). Combined with refined processes such as electron beam lithography, these instruments allow the deliberate manipulation of nanostructures.
General fields involved with proper characterization of nanomaterials include physics, chemistry, and biology, as well as mechanical and electrical engineering.
However, due to the inter- and multidisciplinary nature of nanotechnology, subdisciplines such as physical chemistry, materials science, or biomedical engineering are considered significant or essential components of nanotechnology.
The proper characterization of nanomaterials is a dominant concern of nanotechnologists. The atomic force microscope (AFM) and the Scanning Tunneling Microscope (STM) are two early versions of scanning probes that launched nanotechnology. There are other types of scanning probe microscopy, all based on the idea of the STM, that make it possible to see structures at the nanoscale. This is why scanning probe microscopy has become an important technique for the characterization of nanomaterials. However, all these tools are difficult to handle, require a lot of skill and expertise along with a tedious preparation and furthermore are slow and expensive.
Polymer is a term used to describe molecules consisting of structural units and a large number of repeating units connected by covalent chemical bonds. The key feature that distinguishes polymers from other molecules is the repetition of many identical, similar, or complementary molecular subunits in these chains. These subunits, the monomers, are small molecules of low to moderate molecular weight, and are linked to each other during a chemical reaction called polymerization. Instead of being identical, similar monomers can have various chemical substituents. The differences between monomers can affect properties such as solubility, flexibility, and strength.
Although most polymers are organic, with carbon-based monomers, there are also inorganic polymers; for example, the silicones, with a backbone of alternating silicon and oxygen atoms and polyphosphazenes.
Physical properties of polymers include the degree of polymerization, the molar mass distribution, crystallinity, as well as the thermal phase transitions, branching and stereoregularity or tacticity.
Interestingly, polymer substrates are used for everyday banknotes in Australia, Romania, Papua New Guinea, Samoa, Zambia, Vietnam, New Zealand and a few others, and the material is also used in commemorative notes in some other countries.
The characterization of a polymer requires several parameters which need to be specified. This is because a polymer actually consists of a statistical distribution of chains of varying lengths, and each chain consists of monomer residues which affect its properties. A variety of lab techniques are usually used to determine the properties of polymers. Techniques such as wide angle X-ray scattering, small angle X-ray scattering, and small angle neutron scattering are used to determine the crystalline structure of polymers. Gel permeation chromatography is used to determine the number average molecular weight, weight average molecular weight, and polydispersity. FTIR, Raman and NMR can be used to determine composition.
However, similarly as for silicate materials and nanomaterials these methods require a complex and expensive instrumentation and a good deal of expertise, time and effort.
Nevertheless, in all these applications, the physicochemical characterization of these scientific materials is of great importance. Only well characterized and optimized materials can be used in demanding fields.
Furthermore, in demanding fields it is oftentimes important to make sure that the scientific materials that are used are continuously from the same source to ensure an excellent reproducibility.